The present invention relates to an electromagnetic structure useful as either a position indicator or a differential transformer. More particularly, it relates to such a structure which is quite simple and yet when it is used as a position indicator provides precise measurements of position over a wide range of positions, and when it is used as a differential transformer provides an output electromotive force whose value can be closely controlled.
Electromagnetic position indicators have been designed in the past which rely on a position change causing a corresponding measurable change in the amount of magnetic flux which flows along a closed-loop magnetic flux path. That is, flow of magnetic flux along a path defined by one or more magnetic bodies is caused by a coil interactively associated with such bodies, through which an alternating current is passed. A secondary or "pick-up" coil is also interactively associated with the body to have an electromotive force (emf) generated therein proportional to the amount of flux which flows along the path.
As is known, one of the factors which determines the amount of flux flow is the transverse area of the material through which such flux can flow. Thus, certain electromagnetic position indicators are connected to the mechanism whose position is to be measured so that any position change in the latter will result in a corresponding change in the transverse area of magnetic material and, hence, a change in the generated emf.
Electromagnetic position indicators of this type generally are fairly limited with respect to the range of position change to which they can respond. In this connection, they generally are designed so that a position change will cause a corresponding change in the degree of alignment of the poles of two magnetic bodies forming the closed-loop magnetic flux path. This results in a change in the effective transverse area through which the flux can flow along the path and causes a corresponding change in the value of the emf generated in the secondary coil. It will be recognized that the range of position changes is thereby limited to the area of the opposed pole faces. Typically, a relatively small position change will result in a fairly high change in the percentage of the facing poles in alignment with one another. This is particularly true when the motion change to be sensed is rotary. As a practical matter, with conventional arrangements, the greatest rotation orientation which can be measured is limited to about 60.degree.. While reduction gearing extending between the mechanism whose motion is to be sensed and the position indicator will allow a greater range of motion to be sensed, this greater range is only obtained at the sacrifice of precision in measurement.
A differential transformer is an electromagnetic device in which two secondary coils interactively associated with separate poles of magnetic bodies along two different closed-loop magnetic flux paths are connected in series opposition so that the electromotive force (emf) generated in one of the coils is opposed by the emf induced in the other coil. The result is that the combined emf output represents the difference between the emf's induced in the two secondary coils. It is important for many uses of a differential transformer, that the value of the combined emf output accurately reflects the changes in the magnetic flux paths responsible for the same.